This invention relates to liquid level sensing devices and more particularly to fiber optic liquid level sensing devices.
Due to safety and environmental regulations as well as for other reasons, many tank trucks will have to be filled with hydrocarbons by a bottom loading process. By this method, operators will not be allowed to observe the liquid level since the tank will probably be closed to permit vapor recovery. Therefore, some type of liquid level indicator which can be interfaced with a system for controlling the filling process will be required. When designing a liquid level indicator for hydrocarbon systems, several considerations are important.
The possibility of fire is an ever present danger. For this reason, it is desirable to use equipment that is least likely to cause a spark or to start a fire. While this possibility is extremely remote with most electrical or capacitance sensors, these types of sensors are often best avoided.
The need for a failsafe sensor that can withstand the physical punishment of continuous use is another consideration. Float valves, capacitance probes, and other similar level sensing devices can easily be damaged by continuous abuse, especially if they have moving parts.
Preventing spills is still another problem for safety, economic, and ecological reasons. Reliance on visual aids such as floats is not failsafe since the operator's judgment and alertness is always a factor in preventing spills. Also, with some toxic liquids, when no vapor recovery system is available, the operator should not remain near the liquid while filling the tank. This filling process requires an automatic cut-off when the tank is filled.